The invention relates to an electrographic development station and, more particularly, to such a station having an improved mixer for developer material.
Electrographic apparatus, such as copier/duplicators, have a development station for applying developer material to a latent image on one surface of a photoconductor as the image is advanced past the station. A development station may comprise a sump for holding a supply of developer material, an applicator such as a magnetic brush for supplying such material to the latent image on the photoconductor, and a skive for removing any excess developer material from the applicator and returning it to the sump. The developer material in the sump may comprise a two-component developer consisting of carrier particles and relatively smaller toner particles. A mixer in the sump thoroughly mixes the two-components of the material together to triboelectrically charge the material prior to delivery of the material to the magnetic brush. The mixer may take various forms, including paddle wheel type mixers, augers, etc. It also is known to provide an impeller having a plurality of projecting blades of equal length for delivering developer material from the sump to a magnetic brush. Electrographic apparatus having a development station as generally discussed above is disclosed, for example, in U.S. Pat. No. 3,640,248 issued Feb. 8, 1972 in the name of W. B. Nielander and entitled "Electrostatic Magnetic Developing Apparatus."
Prior development stations have worked satisfactorily for developing latent images on a photoconductor. However, there are some problems with prior development stations. In magnetic brush development apparatus a skive may be provided for deflecting developer material from a shell of the magnetic brush after such material has been passed through a development zone located between the brush and the photoconductor. The material thus removed by the skive has a tendency to cling to the surface of the skive instead of quickly dropping back into the sump of the development station. Any developer material that clings to the skive interferes with removal of additional material from the magnetic brush and return of such material to the sump.
Another problem with development stations of electrographic apparatus is that developer material in the bottom of the sump is difficult to reach and move with existing mixers. As a result, a certain portion of the developer material is effectively not available for developing latent images. Such can be tolerated in development stations having sumps with relatively large capacities; however, for smaller development stations it is important to be able to utilize substantially all of the developer material in the sump so that the sump does not have to be frequently refilled by the machine operator.
A further problem with prior apparatus is that a magnetic brush may accumulate excess developer material in an area spaced from the development zone. Such can result in high torque requirements, eddy currents and high heat in the development station.